A. Technical Field
The present invention relates to an insulated cargo container. In one embodiment, the insulated cargo container is an insulated railroad boxcar.
B. Related Art
Currently, many shippers utilize refrigerated and/or insulated large cargo containers (such as boxcars) to transport items that require the maintenance of specified temperatures during transit. Because these containers are required to maintain certain temperatures, the thermal efficiency of these containers is an important feature. Thermal efficiency is characterized by the thermal conductivity of a particular component or its inverse, its resistance to heat transfer, commonly referred to as an R-value.
The majority of heat loss through these containers occurs through the sidewalls, end walls, doors, roofs, and underframes. Typically, these components are constructed of steel. If the container is a boxcar, it usually has several steel posts on the interior of the car. In order to insulate the cars, wood risers are installed in the side walls, floor, roof, and end walls and between the interior steel posts. Panels of plastic foam, such as urethane, are then placed in the spaces around the wood risers. A liner is then placed over the wood and foam structure. Components of this construction typically possess an R-Value of approximately 6 per inch of foam. More recently, some cargo containers have been constructed from composites in addition to steel and wood, but utilizing similar insulating materials.
Cargo containers of this construction, however, suffer from several drawbacks. In order to adequately insulate the car, a large thickness of wood and foam insulation must be used. This, however, significantly narrows the interior dimensions of the car thereby reducing the amount of cargo that the container can hold. In addition, even with this significant thickness, the thermal efficiency of the container is not as high as would be desired.
Therefore, there is a need for an insulated and refrigerated cargo container having a high insulation value without significantly reducing the interior dimensions of the car.
In addition to including insulation, current cargo containers often include a plenum located on the interior surface of its roof. The plenum allows for air-flow over the roof, which improves the temperature distribution in the cargo container. Typically, the plenums include metallic supports on either longitudinal end of the container and are supported by hangers. Plenums of this design, however may incur damage to the supports caused by impacts due to forklift trucks or pulling out of fasteners.
Therefore, there is a need for a roof plenum design that will be resistant to impact due to forklift trucks or pulling out of fasteners.